Keychain writes silently failed (missing keychain-access-groups entitlement
on simulator), causing the token to disappear between handleTokenResponse
and the first API call. The in-memory cache ensures the token is always
available within the session; the keychain still persists it across launches
when entitlements allow.
iOS clients now exchange the OIDC authorization code for a backend-signed
HS256 JWT via POST /auth/token. All subsequent API requests authenticate
using this JWT as a Bearer token, verified locally — no per-request IDP
call is needed. Web frontend session-cookie auth is unchanged.
